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Open AccessArticle

Impacts of River Engineering on River Channel Behaviour: Implications for Managing Downstream Flood Risk

1
AquaUoS, University of Salford, Salford M5 4WT, UK
2
School of Science, Engineering and Environment, University of Salford, Salford M5 4WT, UK
*
Author to whom correspondence should be addressed.
Water 2020, 12(5), 1355; https://doi.org/10.3390/w12051355
Received: 30 March 2020 / Revised: 4 May 2020 / Accepted: 5 May 2020 / Published: 11 May 2020
(This article belongs to the Special Issue Fluvial Geomorphology and River Management)
Although knowledge of sediment transport has improved over the last 25 years, our understanding of bedload transfer and sediment delivery is still based on a limited set of observations or on models that make assumptions on hydraulic and sediment transport processes. This study utilises repeat lidar survey data of the River Caldew above the City of Carlisle in the UK to investigate the balance of erosion and deposition associated with channel switching from an engineered and managed single thread channel to a naturalising incipient wandering system. Over the 11-year survey period (four bankfull flood events) around 271,000 m3 of sediment were delivered to the river and floodplain and 197,000 m3 eroded suggesting that storage rates of around 7000 m3/annum occurred. The balance of erosion and deposition is influenced by channelisation with very restricted overbank sedimentation and only limited local and transient in-channel bar deposition along the engineered reach (8000 m3 eroded). This contrasts with the activity of the naturalising reach downstream where a developing wandering channel system is acting to store coarse sediment in-stream as large bar complexes and the associated upstream aggrading plane bed reaches and overbank as splay deposits (87,000 m3 stored). Such behavior suggests that naturalisation of channelised systems upstream of flood vulnerable urban areas can have a significant impact on sediment induced flooding downstream. This conclusion must, however, be moderated in the light of the relatively small volumes of material needed to instigate local aggradation in over-capacity urban channels. View Full-Text
Keywords: flooding; lidar; wandering; natural sediment management; natural flood management flooding; lidar; wandering; natural sediment management; natural flood management
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MDPI and ACS Style

Heritage, G.; Entwistle, N. Impacts of River Engineering on River Channel Behaviour: Implications for Managing Downstream Flood Risk. Water 2020, 12, 1355.

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